NAME

arp − Displays and controls Address Resolution Protocol (ARP) tables

SYNOPSIS

/usr/sbin/arp [−u] hostname

arp −a [−u] [−n] [system]

arp −d hostname

arp −f filename

arp −g hostname

arp −s [−u] hostname hardware_addr [temp] [pub] [trail]

FLAGS

−aDisplays all of the current ARP entries. 

−d hostname
Deletes the entry for hostname if the user issuing the command has superuser authority. 

−f filename
Reads entries from filename and adds those entries to the ARP tables.  Use of this flag requires superuser privilege.  Entries in the file have the following format:

hostname hardware_addr [temp] [pub] [trail]

Fields in this format are as follows:

hostname
Specifies the remote host identified by the entry.

hardware_addr
Specifies the hardware address of the remote host. The address is given as 6 hexadecimal bytes separated by colons.

tempSpecifies that this ARP table entry is temporary.  When this argument is not used, the table entry is permanent. 

pubIndicates that the table entry will be published and that the current system will act as an ARP server, responding to requests for hostname even though the host address is not its own. 

trailIndicates that the trailer encapsulation may be sent to this host. 

−nDisplays numeric IP addresses and hardware addresses only.  When this flag is not specified, arp displays hostnames, numeric IP addresses, and hardware addresses. 

−g hostname
Sends a gratuitous ARP packet.  The hostname can be a local host name, alias, or IP address. 

−s hostname hardware_addr [temp] [pub] [trail]
Creates a single ARP entry for hostname.  Use of this flag requires superuser privilege.  The arguments are explained in the discussion of the −f flag. 

[−u]Displays the MAC address in noncanonical form with address bytes reversed and separated by a colon character (:). By default, all addresses are displayed in canonical form with address bytes separated by the hyphen character (-). 

When used with the −s flag, this indicates that the hardware_addr is in noncanonical form. 

DESCRIPTION

The arp command displays or modifies the current ARP entry for the host specified by hostname.  The host may be specified by name or number, using Internet dot notation. 

With no flags, the program displays the current ARP entry for hostname. 

The ARP tables can be displayed by any user, but only the superuser can modify them. 

EXAMPLES

     1.To display the ARP address-mapping tables for the local host that has one interface defined, enter:

arp -a
alpha1.dec.com (16.181.20.2) at 08-00-2b-2c-f5-31
alpha2.dec.com (16.100.21.20) at 08-00-2b-3c-2d-fd

     2.To add a single entry for the remote host laszlo to the ARP mapping tables temporarily, enter:

arp -s laszlo 08:00:2b:0f:44:23 temp

The address is considered canonical even though the bytes are separated by colons. For input, the arp command does not use the colon (:) and hyphen (-) characters to indicate whether the address is canonical or noncanonical. 

Note that you must have superuser authority to execute this command. 

     3.To add a single entry for the remote host laszlo to the ARP mapping tables temporarily, enter:

arp -u -s laszlo 10:00:d4:f0:22:c4 temp

The −u flag indicates the address is noncanonical. Note that you must have superuser authority to execute this command. 

     4.To add multiple entries to the ARP mapping tables from the file newentries, enter:

arp -f newentries

Note that you must have superuser authority to execute this command. 

FILES

/usr/sbin/arpSpecifies the command path. 

RELATED INFORMATION

Commands: netstat(1), ifconfig(8)

Protocols: arp(7)

Specifications:  RFC 826